The present invention relates to turbocharging systems and, more particularly, to a turbocharger for use on two-cycle engines wherein oil mist is drawn from the crankcase to lubricate ball bearings supporting the shaft of the turbocharger during idle and low RPM and fuel/oil mixture is drawn through the bearings and into the air being pressurized by the compressor of the turbocharger to simultaneously lubricate the bearings while providing a source of enriching fuel mixture to the engine during turbine boost.
Recently, turbocharging has become a very common method of obtaining additional power from engines. While superchargers of the mechanical type were large, noisy, expensive, and cumbersome, modern turbochargers, driven by exhaust gases, are small, relatively inexpensive, light weight, and easily incorporated on a multitude of vehicles from motorcycles to luxury sedans. The addition of a turbocharger to a typical 235 horsepower production V-6 outboard engine, for example, can increase the peak power from 235 SAE horsepower at 5800 RPM to 330 SAE horsepower at 6800 RPM with approximately one atmosphere of pressure boost.
Turbobchargers obtain their performance by using speed instead of size. A shaft is provided with a turbine on either end. Exhaust gases are conducted to drive the one turbine to thereby spin the shaft and the opposite turbine which is used to draw in and compress air which is then used as part of the air/fuel mixture of the engine. To obtain the pressures and flow volumes required, a typical turbocharger may idle at or about 10,000 RPM and reach speeds of 20,000-80,000 RPM as its operating speeds. As can be realized, between the operating speeds and the fact that the metal components are being driven by hot exhaust gases from the engine, cooling and lubrication of the shaft and bearings supporting the two turbines becomes a major problem. With a four-cycle engine, the problem can be solved since there is a source of circulating oil which can be routed to cool and lubricate the shaft and its conventional floating bushings.
Two-cycle engines, on the other hand, provide a severe problem to the effective incorporation of a turbocharger boosting system. The typical valves, camshaft, etc., of the four-cycle engine are missing, as is the pressurized oil system utilized to lubricate those members. The lower members of the engine components, the upper cylinder walls, and the like, are lubricated by mixing oil in with the gasoline.
An additional consideration with all turbocharger systems is the requirement for enriching the fuel as the boost pressure rises.
To date, no one has successfully solved the above-described problems for two-cycle engines. A partial solution is shown in FIG. 1 which corresponds to FIG. 2 from U.S. Pat. No. 3,200,580 of G. H. Millar. In the Millar apparatus, the turbocharger, generally indicated as 10, has a housing 12 supporting a shaft 14 therein on a pair of ball bearings 16 for rotation. One end of the shaft 14 is connected to a turblne 18 which is rotated by exhaust gases 20 entering at 22 and exiting at 24. The opposite end of shaft 14 is connected to a compressor 26 which draws air 28 in at 30 and outputs pressurized air 32 through conduit 34 which is connected to the air intake of carburetor 36. There is a seal 38 at the air end of the shaft 14 and another seal 40 at the exhaust end of the shaft 14. Thus, the ball bearings 16 within the housing 12 are contained within a compartment 42 completely sealed off from either of the turbines 18, 26. To provide lubrication and cooling, the gasoline line 44 normally connected between the fuel pump 46 and the carburetor 36 is broken and routed to pass the fuel/oil mixture, as indicated by the arrows 48, through compartment 42 to cool and lubricate the ball bearings 16. The fuel/oil mixture 48 enters through passageway 50, passes through the two bearings 16, and exits through passageway 52. This system has several shortcomings. Firstly, no ball bearing system should be operated at high speed with the bearings submerged as severe foaming would occur. Secondly, Millar's design would require a liquid tight seal at each end of the shaft. No seal is presently available that would stand both the speed (80,000 plus RPM) and temperature (1300+F.) at the turbine end of the shaft. Also, the use of submerged bearings would cause undesirable drag on the bearings and rotating assembly. Additionally, any contaminants introduced into the fuel/oil mixture 48 within the turbocharger 10 would be passed on to possibly clog the carburetor 36. Finally, no provision is made for fuel enriching.
Wherefor, it is the object of the present invention to provide a practical method of lubricating the supporting shaft and bearings of a turbocharger used on two-cycle engines while, simultaneously, providing an automatic means for enriching the fuel mixture in relation to boost pressures being applied.